CI: check for potential translation errors

Some warnings in the generation of the translation files indicate real
errors, like strings that cannot be extracted for translations. Check
that no warnings are emitted.

.gitlab-ci.yml

@@ -57,11 +57,11 @@ variables:
   #
   # This is done by running `ci-fairy generate-template` and possibly bumping
   # ".default_tag".
-  ALPINE_TAG:  'tag-b51da9e3f95a'
-  CENTOS_TAG:  'tag-c89e0aac1363'
-  DEBIAN_TAG:  'tag-76973ff363a5'
-  FEDORA_TAG:  'tag-c89e0aac1363'
-  UBUNTU_TAG:  'tag-76973ff363a5'
+  ALPINE_TAG:  'tag-7da44bbacc09'
+  CENTOS_TAG:  'tag-c8090b8a9a6b'
+  DEBIAN_TAG:  'tag-86a16c2d74d8'
+  FEDORA_TAG:  'tag-c8090b8a9a6b'
+  UBUNTU_TAG:  'tag-86a16c2d74d8'
 
   ALPINE_EXEC: 'bash .gitlab-ci/alpine-install.sh'
   CENTOS_EXEC: 'bash .gitlab-ci/fedora-install.sh'
@@ -710,6 +710,7 @@ check-tree:
     - date '+%Y%m%d-%H%M%S'; git ls-files -z -- 'po/*.po' | xargs -0 -n1 msgfmt -vc
     - date '+%Y%m%d-%H%M%S'; contrib/scripts/nm-code-format.sh -n
     - date '+%Y%m%d-%H%M%S'; ci-fairy generate-template && git diff --exit-code
+    - date '+%Y%m%d-%H%M%S'; ./autogen.sh && [ "$(LANG=C make -C po update-po 2>&1 1>/dev/null | grep -c 'warning:')" = 0 ]
 
 pages:
   stage: deploy

.gitlab-ci/ci.template

@@ -209,6 +209,7 @@ check-tree:
     - date '+%Y%m%d-%H%M%S'; git ls-files -z -- 'po/*.po' | xargs -0 -n1 msgfmt -vc
     - date '+%Y%m%d-%H%M%S'; contrib/scripts/nm-code-format.sh -n
     - date '+%Y%m%d-%H%M%S'; ci-fairy generate-template && git diff --exit-code
+    - date '+%Y%m%d-%H%M%S'; ./autogen.sh && [ "$(LANG=C make -C po update-po 2>&1 1>/dev/null | grep -c 'warning:')" = 0 ]
 
 pages:
   stage: deploy